How strange. I also noted that Le Grand has been pulled from my BRG site.
I have, however, had more luck with my claim. Less than a day after the generic BRG "contacting the hotel" email, I received an amended reservation confirmation from IHG with:
Rate Description:
HOUSE USE COMP
Rate Type:
HOUSE USE COMP
for my stay at Le Grand in December.
Good luck to anyone having trouble with this one though - I would suggest you get on the phone to the BRG people and ask for an explanation. Once they verify it then in theory the hotel should not be able to decline it provided the BRG agent hasn't messed up the claim somehow (which I highly doubt as they seem to be incredibly meticulous). Regardless, in my opinion you should get your complimentary first night no matter whether IHG or the hotel loses out: it's not the guest's problem and you have simply taken advantage of their guarantee, to which you have remained within the terms and conditions.
My surmisal is that they have been inundated with BRG requests over the last week and are taking a stand against giving their supposedly high-value rooms away for zero centimes. Sacrebleu.